PYROTHERUM 165 



character, being oval in cross section and having enamel 

 on the front face only. These first incisors are directed 

 downward, so that their ends stand between and very 

 slightly in front of the second incisors. The end of each 

 is worn bluntly round in contrast to the beveled end of 

 inc. 2. The second incisor is larger, rootless, and perma- 

 nently growing, with a hollow base, enamel on the front 

 face only, and oval in cross section. Both these teeth 

 have a layer of cement on them, extending some distance 

 beyond the alveolus. The tips are worn in a long bevel 

 on the posterior side, very much as is the case on the 

 incisors of rodents. 



The third upper incisor, the canine, and premolar 1 

 are lacking, a long diastema occupying their place, out 

 of which they have been crowded by the development 

 of the enormous root of inc. 2, which extends 150 mm. 

 and more back into the jaw. P. romeri is distinguished 

 from the others by pm. 1 being present. 



The teeth of the upper premolar-molar series have their 

 crowns expanded, and the two series of either side have 

 moved toward each other; until in front they are in con- 

 tact while in the rear they are only 50 mm. apart, narrowing 

 the palate in a unique manner, and giving the impression 

 that the palate is mostly a grinding surface. The pre- 

 molars are completely molariform and the whole series 

 is at an advanced stage of specialization. 



Premolar 2 is three- rooted, with a triangular crown on 

 which are three mamma-like tubercles, the larger one in 

 front, and two behind. As the crown is worn, these unite 

 into a flat, grinding surface, surrounding a central pit 

 which opens behind. Premolars 3 and 4 and all the molars 

 are large, four-rooted, quadrilateral teeth, each with two 

 transverse crests running clear across the crown, and with 

 a small cingulum across the anterior margin. Before they 

 are worn, the top of each crest is tuberculated, and the 

 cingulum is crenulated. In wearing, the anterior face 



